implement some sort of simple exception chaining.

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.3.0-dev.1
+
+* Support for exception chaining.
+
 ## 1.2.0+1
 
 * Graylog: Send timestamp with decimal places.

example/pubspec.lock

@@ -63,7 +63,7 @@ packages:
       path: ".."
       relative: true
     source: path
-    version: "1.2.0+1"
+    version: "1.3.0-dev.1"
   meta:
     dependency: transitive
     description:

lib/src/exception_chain.dart

@@ -0,0 +1,35 @@
+// based on https://github.com/dart-lang/language/issues/2119#issuecomment-1042365842
+
+final Expando<ErrorStack> _causedBy = Expando();
+T _wasCausedBy<T extends Exception>(
+    T target, Object cause, StackTrace causeStackTrace) {
+  _causedBy[target] = (error: cause, stack: causeStackTrace);
+  return target;
+}
+
+typedef ErrorStack = ({Object error, StackTrace stack});
+
+/// Allow exception chaining.
+/// example:
+/// ```
+/// try {
+///   ...
+/// } on Exception (e, stackTrace) {
+///   throw
+/// }
+extension CausedByException<E extends Exception> on E {
+  E causedBy(Object chainedException, StackTrace stackTrace) =>
+      _wasCausedBy(this, chainedException, stackTrace);
+  ErrorStack? getCausedByException() => _causedBy[this];
+
+  String toStringWithCause() {
+    final cause = this.getCausedByException();
+    if (cause == null) {
+      return toString();
+    }
+    final error = cause.error;
+    final causeToString =
+        error is Exception ? error.toStringWithCause() : error.toString();
+    return '${toString()} cause: {$causeToString}';
+  }
+}

lib/src/logrecord_formatter.dart

@@ -1,4 +1,5 @@
 import 'package:logging/logging.dart';
+import 'package:logging_appenders/src/exception_chain.dart';
 import 'internal/ansi.dart' as ansi;
 
 /// Base class for formatters which are responsible for converting
@@ -39,18 +40,27 @@ class DefaultLogRecordFormatter extends LogRecordFormatter {
     sb.write('${rec.time} ${rec.level.name} '
         '${rec.loggerName} - ${rec.message}');
 
-    if (rec.error != null) {
-      sb.writeln();
-      sb.write('### ${rec.error?.runtimeType}: ');
-      sb.write(rec.error);
-    }
-    // ignore: avoid_as
-    final stackTrace = rec.stackTrace ??
-        (rec.error is Error ? (rec.error as Error).stackTrace : null);
-    if (stackTrace != null) {
-      sb.writeln();
-      sb.write(stackTrace);
+    void formatErrorAndStackTrace(final Object? error, StackTrace? stackTrace) {
+      if (error != null) {
+        sb.writeln();
+        sb.write('### ${error.runtimeType}: ');
+        sb.write(error);
+      }
+      // ignore: avoid_as
+      final stack = stackTrace ?? (error is Error ? (error).stackTrace : null);
+      if (stack != null) {
+        sb.writeln();
+        sb.write(stack);
+      }
+      final causedBy = error is Exception ? error.getCausedByException() : null;
+      if (causedBy != null) {
+        sb.write('### Caused by: ');
+        formatErrorAndStackTrace(causedBy.error, causedBy.stack);
+      }
     }
+
+    formatErrorAndStackTrace(rec.error, rec.stackTrace);
+
     return sb;
   }
 }

pubspec.yaml

@@ -1,6 +1,6 @@
 name: logging_appenders
 description: Logging appenders for the dart logging package for print, file and remote (logz, loki, graylog (gelf)).
-version: 1.2.0+1
+version: 1.3.0-dev.1
 homepage: https://github.com/hpoul/dart_logging_appenders/
 screenshots:
   - description: Colored console output
@@ -18,8 +18,15 @@ dependencies:
 
 dev_dependencies:
   test: ^1.25.2
+  matcher: ^0.12.16+1
   lints: ^3.0.0
   mockito: ^5.4.4
   fake_async: ^1.3.1
   path: ^1.8.3
   build_runner: ^2.4.8
+
+topics:
+  - logging
+  - logger
+  - error
+  - console

test/exception_chain_test.dart

@@ -0,0 +1,26 @@
+import 'package:logging_appenders/logging_appenders.dart';
+import 'package:logging_appenders/src/exception_chain.dart';
+import 'package:test/expect.dart';
+import 'package:test/scaffolding.dart';
+
+import 'package:logging/logging.dart';
+
+final _logger = Logger('exception_chain');
+
+void main() {
+  PrintAppender.setupLogging();
+  test('Simple chained exception', () {
+    try {
+      try {
+        int.parse('a');
+      } catch (e, stackTrace) {
+        throw Exception('unable to parse').causedBy(e, stackTrace);
+      }
+      fail('unreachable');
+    } on Exception catch (e, stackTrace) {
+      expect(e.getCausedByException(), isNotNull);
+      expect(e.getCausedByException()?.error, isFormatException);
+      _logger.finer('catched exception.', e, stackTrace);
+    }
+  });
+}